Low oil level control device for hydraulic lifts



A ril 20, 1965 I. v. K. HOTT EI'AL LOW OIL LEVEL CONTROL DEVICE FOR HYDRAULIC LIFTS Filed May 7, 1962 a: WW w m w M flmNM 4 mW M United States Patent 3,179,014 LOW OIL LEVEL CONTROL DEVICE FOR HYDRAULIC LIFTS Ion V. K. Hott and David M. Goldzwig, Dayton, Ohio, assignors to The Joyce-Cridland Company, Dayton, Ohio, a corporation of Ohio Filed May 7, 1962, Ser. No. 192,911 2 Claims. (Cl. 91-4) This invention relates to a lift structure and, more particularly, to a low level oil control for hydraulic lifting mechanisms.

An object of this invention is to provide an improved automatic low oil control for lifting mechanisms.

A further object of this invention is to provide and improved structure for controlling the movement of a lift piston in a semi-hydraulic lift of the type in which air under pressure is introduced into the lift piston above a body of liquid therein through an air tube projecting upwardly through the base of the piston, the liquid being forced through a liquid passageway in the piston base, causing the piston to rise relative to the cylinder.

Another object of this invention is to provide structure for automatically preventing continued rise of the lift piston in the aforementioned type of semi-hydraulic lift in the event the level of liquid within the :piston becomes so low as to allow air to escape from the lift piston through the liquid passageway provided in the piston base.

Still another object of this invention is to provide a method for guarding against inadvertent operation of a hydraulic lift before it is filled with the usual supply of liquid.

Other objects and advantages reside in the construction of parts, the combination thereof, the method of manufacture and the mode of operation, as will become more apparent from the following description.

Referring to the drawing:

FIGURE 1 is an elevational view, with portions broken away and in cross-section, of a semi-hydraulic lift mechanism provided with low level oil control means made in accordance with this invention. In FIGURE 1, the piston is shown in its lowermost position relative to the cylinder just after assembly and before introduction of liquid therein.

FIGURE 2 is an elevational view similar to FIGURE 1 illustrating the lift piston in a raised position relative to the cylinder.

FIGURE 3 is an enlarged cross-sectional view of the portion of the lift mechanism, with parts broken away, enclosed within the view line 3 of FIGURE 1.

FIGURE 4 is an enlarged cross-sectional view of the portion of the lift mechanism, with parts broken away, enclosed within the view line 4 of FIGURE 2.

In the drawing, the invention is shown as incorporated in a vehicle lift comprising a piston mounted for vertical movement within a cylinder 12. The cylinder 12 normally would be in a pit in the ground with its upper end slightly above ground level and a vehicle engaging superstructure (not shown) normally would be attached to a top cover plate 14 for the piston 10. The top cover plate 14 of the piston 10 completely closes its upper end while a base plate 16 closes its lower end. As well known, the cover plate 14 is removable to provide access to parts located within the piston 10. In this case, the plate 16 is shown as generally in the form of a truncated cone having its base welded adjacent the lower end of the wall of the piston 16. To permit liquid to pass through the piston base plate 16, a metering structure 18 is carried thereby in covering relation to an aperture 20 therein. An annular flange 22 may be provided adjacent the top of the cylinder 12 to fix it in position relative to the ground "ice while the base of the cylinder 12 is closed by a base plate 24 welded to the wall thereof. The cylinder 12 may be supported by struts 26 upon a base fixture 28 mounted within the pit in which the cylinder is located.

After installation of the type of lift mechanism described above, the piston 10 and cylinder 12 are filled nearly full with a suitable viscous liquid, usually oil, through a fill plug 30 located in the cover plate 14. To completely fill the cylinder 12 around the piston 10, a bleeder valve 32 is mounted near the top of the cylinder 12 to permit air to :pass therethrough. In operation, air under pressure is supplied to the top of the piston through an air tube 34 projecting longitudinally therethrough, which communicates with an air inlet port 36 located in the base fixture 28. The compressed air forces the liquid in the piston 10 through the metering structure 18 into the cylinder 12, in turn forcing the piston upwardly.

The air tube 34 passes centrally through the cylinder base plate 24 and through the aperture 20 in the piston base plate 16 and is supported in an upright position by a generally conical support member 40 secured to the cylinder base plate 24. To protect the air tube 34 during shipping, a conical shipping protector 42 is attached to the pottom surface of the piston cover plate 14. The member 42 also serves as a baffle to supply compressed air equally in all directions when the piston is initially raised.

The piston 10 is held in spaced relation to the cylinder 12 by means including a conventional bearing structure, packing members, a wiper element and so forth. These elements are well-known and may take any conventional form. Since they form no part of this invention, they are not disclosed herein. The rise of the piston 10 relative to the cylinder 12 may be limited by engagement of an annular flange 44 on the bottom of the piston 14 with an annular stop 46 attached to the internal surface of the cylinder 12 in the upper portion thereof. The stop 46 may form .part of the bearing structure used to guide the movement of the piston 10.

The speed with which the piston is raised and lowered is directly dependent upon the rate of liquid flow through the aperture 20 in the piston base plate 16. To limit the speed of movement of the piston, the metering structure 18 comprises a spindle or sleeve 50 encircling the air tube 34. An upper seal plate 52 is connected to the upper end of the sleeve or spindle 50 and a lower seal plate 54 is connected to the lower portion of the member 50. As shown most clearly in FIGURE 4, the upper seal plate 52 may be integral with the sleeve 50. The lower end of the sleeve 50 is of a reduced diameter to receive the lower seal plate 54, which is fixed between a shoulder formed at the top of the reduced portion of the sleeve 51) and a snap rnig 55 encircling the sleeve 50. The lower seal plate 54 includes a central, depending hub portion 56 provided with an annular recess for receiving the upper end of a conically coiled spring 58 for purposes which will be described below. The upper seal plate 52 is adapted to seat upon the top surface portion of the base plate 16 adjacent the aperture Zti while the lower seal plate 54 is similarly adapted to engage the bottom surface of the piston base plate 16. Thus, the seal plates 52, 54 are separated by the portion of the sleeve 50 therebetween and are held in a generally parallel, spaced relation at a separation greater than the thickness of the base plate 16.

Liquid passes through the metering structure 18 in the following fashion. The internal diameter of the spindle or sleeve 50 is greater than the external diameter of the air tube 34 whereby an annular fluid passageway 60 is formed between these two elements. Desirably, the difference in the diameter of the .bore in the member 50 and the external diameter of the air tube 34 is comparatively small so that the metering structure 18 is not too loosely received upon the air tube 34. In order to have a satisfactorily small fluid passageway 60, a pair of apertures 62, extending transversely through the sleeve 50 between the seal plates 52 and 54, provide transverse fluid passageway communicating with the longitudinal fluid passageway 60.

The flow of liquid through the aperture 20 is further controlled by a buoyant valve member 70 comprising a pair of floats 72 mounted in diametrically opposed relation upon a valve base plate having a pair of arms 74 projecting horizontally from a sleeve 76 supported on the air tube 34 in surrounding relation thereto. The floats 72, desirably, are of a hollow, lightweight metal construction with sufliciently strong sidewalls to prevent their collapse under pressure and are adequately resistant to deterioration in the oil. These floats may be made of magnesium and may be of the type described in Patent No. 2,763,128, issued to Ion V. K. Hott, on September 18, 1956, The floats 72 may be secured to the arms 74 as by screws 38 in threaded engagement with the arms 74 and an internal boss formed within the floats. Again, the diameter of the bore within the sleeve 76 is such that the valve member 74 is only loosely received on the air tube 34. Accordingly, the valve member 70 may freely float above the base plate 16.

In the drawings, the valve member 70 is shown seated upon the top surface of the spindle or sleeve 50 of the metering structure 18. Under normal conditions, it is to be understood that the valve member 70 will float in the oil well above the metering structure 13. A baflie member 78 may be mounted in encircling relation to the air tube 34 adjacent its upper end. The baflle 7 8 is preferably elastomeric and serves as a bumper or stop for the valve member 70 preventing it from possible damage caused by its floating upwardly into engagement with the base of the cover plate 14 or the baifle 42. I The metering structure 18 and the valve member 70 function in the following manner. Normally, the valve member 70 floats high in the oil in the piston 10 and is in engagement with the baffle 78. If the piston 10 is being elevated, the upper seal plate 52, due both to gravity and to the pressure exerted by the liquid thereabove, is seated upon the top of the piston base plate 16. A restricted liquid flow is permitted through the longitudinal, annular passageway 60 and the transverse passageways 62 into the cylinder 12 beneath the piston 10. The liquid flow will be both around the lower seal plate 54 and through the lower portion of the spindle or sleeve 50. Thus, a controlled rate of liquid flow is permitted through the aperture 20 while the piston 10 is being elevated. When the piston 10 is being lowered, substantially the same result is obtained. However, in this case, the lower seal plate 54 is engaged with the bottom portion of the piston base plate 16 while the upper seal plate 52 is elevated slightly above the piston base plate 16. According- 1y, liquid passes from the cylinder 12 into the piston 10 through the lower portion of the passageway 60 and thence both through the upper portion of the passageway 60 and through the aperture 62 around the upper seal plate 52.

The valve member 70 functions only when the liquid level within the piston 10 becomes so low that air might otherwise be permitted to pass through the metering structure 18. If this should happen, the control over the speed of movement of the piston 10 is lost and the piston, if being raised, would be forced upwardly at an undesirably high speed. Moreover, the stable support provided by the oil within the cylinder 12 would be lost since the piston 10 would be supported solely by air. Similar problems would be incurred in lowering the lift piston 10. The purpose of the valve member 70, then, is to prevent the passage of air through the metering struc ture 18.

Normally, the valve member 70 floats at or near the top of the level of oil within the piston, except as limited by the baffle 78. Should the oil level become so low relative to the plate 16 as to permit the base of the sleeve portion 76 of the valve member 70 to come into contact with the metering structure 18, the bottom surface of the sleeve 76 will seat against the top surface of the sleeve or spindle portion 56 of the structure 18. Such a condition is shown in FIGURE 4, wherein a low oil condition has been reached just prior to the engagement of the annular flange 44 with the stop member 46. As already described, the upper seal plate 52 is seated on the base plate 16 and the sleeve '76 of the valve member 70 is seated on the top surface of the metering structure 18. Thus, neither fluid nor air can pass under the valve member 70 or the upper seal plate 52.

Also, as noted before, the sleeve 76 is loosely slidable on the air tube 34 and oil could pass between the sleeve 76 and the air tube 34 into the fluid passageway 6t). To avoid this, an elastomeric O-ring sealing member 80 is loosely supported within an annular recess cut internally of the sleeve 76. Under normal conditions, there is no pressure against the O-ring 86 causing it to seal against the air tube 34. However, a plurality of small fluid passageways 82 communicate between the recess within the sleeve 76 and the exterior surface thereof. The fluid passageways 82 are angularly directed downwardly to the top of the O-ring 86 and the lower surface of the recess within the sleeve 76 slopes downwardly at approximately the same angle. In the event the sleeve 76 is seated on the metering structure 18 as shown in FIG- URE 4, there will be a greater pressure above the valve member 70 than below the valve member. Accordingly, the O-ring 80 is forced by the fluid passing through the passageways 32 downwardly into sealing engagement with the air tube 34-. Once this seal is completed, flow of oil downwardly from the piston into the cylinder is prevented and the piston cannot be further elevated simply by introduction of air through the tube 34.

Two floats 72 rather than just a single float are presently preferred so that floats of reasonably small size might be used, yet the combined specific gravity of the floats and the valve base plate is less than the oil used to raise the piston. As apparent, however, a single metal float designed to encircle the air tube 34 could be used so that the valve member '70 would be adequately balanced. By utilizing diametrically opposed floats, which are symmertically disposed relative to the center of gravity of the valve base plate, the member 70 is adequately balanced about a vertical axis so that the valve member will not bind against the air tube 34 when in use. Of course, three floats spaced at equal radii from the vertical axis of the member 70 and disposed one from the other could be used for greater balance.

A unique problem is presented when the lift mechanism is first installed. Ordinarily, the mechanism will be installed truth the component parts in place, but with no oil therein, or, as will be described below, a very low level of oil. The most convenient location for a fill plug is, as shown in FIGURE 1, in the cover plate 14 of the piston 10. When oil is first introduced into the piston 10 through the fill plug, the pressure created by the oil filling the piston would cause the valve member 70 to occupy the position shown in FIGURE 3 wherein it is in sealing engagement with the air tube 34 and the metering structure 18. To permit passage of oil through the metering structure 18 into the cylinder 12 in this circumstance, the spring 58 serves as an abutment means engaging the air tube support member 40 and, accordingly, biasing the metering structure 18 and the valve member 70 upwardly. Oil is therefore permitted to pass between the piston base plate '16 and the upper seal plate 52 through the apertures 62 downwardly through the longitudinal passageway 60 into the cylinder 12. Of course, once the piston 10 and cylinder 12 are fully supplied with oil, the valve member 70 will rise into engagement with the battle 78. Thereafter, operation of the mechanism can continue as described above. The function of the spring 58 is quite important, but is limited to the filling of the lift mechanism with oil either after installation or after repair.

The structure described above has been tested and been found quite satisfactory in operation. Note that if there is a low oil condition, the piston still can be elevated until such time as the valve member 70 seats oh the metering structure 18. By releasing the air above the piston 10 to atmosphere, the downward pressure on the O-ring '80 is removed. Accordingly, the O-ring 80 will be released from sealing engagement with the air tube 34 and the valve member 70 can again float. The piston 10 thereby lowers as under normal operating conditions. Thus, the lift mechanism can be used, although with not such a high rise, until such time as the lost oil within the mechanism is replenished. 1

As noted above, the floats are desirably made of magnesium. The valve base plate, including the arms 74 and the sleeve 76 and also the metering structure 18, may be made of aluminum or other suitable metal. Although a metal-to-metal seal is used between the seal plate 52 and the piston base plate 16, and again between the valve member 70 and the metering structure 18, the seals formed thereby have been found quite adequate to prevent the flow of oil therethrough. However, dry metalto-metal seals will not be sufficient to prevent the flow of air. Since, during ordinary operation, there is always some level of oil within the mechanism, the metering structure 18 and the valve member 70 normally function to safely prevent air from passing into the cylinder 12. However, as noted above, lift mechanisms of this type are usually installed with no oil in them. If, through inadvertence, one should attempt to raise the piston 16 by suppling air under pressure thereto through the air tube 34 before the lift is filled with oil, the piston 10 would be raised at an undesirable and unsafe high speed. This could be quite dangerous, possibly causing injury not only to the lift equipment and perhaps a vehicle intended to be raised thereby, but also to persons who may be standing near the equipment. p

This problem can be avoided, however, during assembly of the lift mechanism before installation in the ground, by filling the lift mechanism with a very low level of oil just sufiicient to coat the metering structure 18 and a portion of the valve member 70 with oil. Such a low level of oil does not appreciably 'add to the weight of the lift mechanism and, accordingly, does not materially afiect the cost of shipping. Since the lift mechanism would then be installed with a low level of oil, the low oil control valve member 70 would seat on the metering structure 18 and the O-ring 80 would immediately seal,

against the air tube 34 should air under pressure be inadvertently introduced into the piston 10. In practice, lift mechanisms of this type are normally assembled, and then tested at the factory with the same amount of oil used during normal operation. The oil used in the test is then flushed out of the mechanism. Simply by incompletely flushing the oil out of the mechanism, a low level of oil is retained therein, thus insuring dependable and safe operation of the mechanism even when first, installed without a full supply of oil.

Although the presently preferred embodiment of the device has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

, Having thus described our invention, we claim:

1. In a lifting mechanism wherein a hollow piston is slidably mounted within a cylinder, the piston and cylinder being substantially filled with a liquid, the piston having a base plate which is apertured to provide fluid communication between the piston and the cylinder, the piston being raised relative to the cylinder by the introduction of air under pressure above the top level of liquid within the piston through a tube projecting upwardly through said aperture into said piston, apparatus for covering said aperture in the event the liquid level within the lift should become so low as to otherwise permit air to pass through said aperture, comprising: a metering structure including at least one seal plate carried by said base plate in covering relation to said aperture, said seal plate being provided with a central aperture slidably receiving said tube, said metering structure further including a lower seal plate disposed beneath said piston base plate, means interconnecting said first mentioned seal plate and said lower seal plate holding said plates in fixed position one with respect to the other such that the separation between the opposed faces thereof is greater than the thickness of said base plate, and abutment means connected to the lower portion of said metering structure adapted to engage a part fixed in relation to the base of the cylinder when the piston is lowered thereby holding the lower surface of said first mentioned seal plate above said base plate; and a buoyant valve member having a longitudinal bore slidably receiving said tube and adapted to float in the liquid above said seal plate, said valve member having a lower surface portion adapted to engage the top surface of said seal plate in surrounding relation to the aperture therein when the liquid in said piston falls'to a low level, and means preventing the passage of liquid through the bore in said valve member when said valve member engages said seal plate.

2. 'The structure of claim 1 wherein said means interconnecting said seal plates comprises a sleeve surrounding said tube and wherein said abutment means comprises I a coil spring connected to the lower portion of said sleeve.

FRED E. ENGELTHALER, Primary'Expminer.

KARL J. ALBRECHT, Examiner. 

1. IN A LIFTING MECHANISM WHEREIN A HOLLOW PISTON IS SLIDABLY MOUNTED WITHIN A CYLINDER, THE PISTON AND CYLINDER BEING SUBSTANTIALLY FILLED WITH A LIQUID, THE PISTON HAVING A BASE PLATE WHICH IS APERTURED TO PROVIDE FLUID COMMUNICATION BETWEEN THE PISTON AND THE CYLINDER, THE PISTON BEING RAISED RELATIVE TO THE CYLINDER BY THE INTRODUCTION OF AIR UNDER PRESSURE ABOVE THE TOP LEVEL OF LIQUID WITHIN THE PISTON THROUGH A TUBE PROJECTING UPWARDLY THROUGH SAID APERTURE INTO SAID PISTON, APPARATUS FOR COVERING SAID APERTURE IN THE EVENT THE LIQUID LEVEL WITHIN THE LIFT SHOULD BECOME SO LOW AS TO OTHERWISE PERMIT AIR TO PASS THROUGH SAID APERTURE, COMPRISING: A METERING STRUCTURE INCLUDING AT LEAST ONE SEAL PLATE CARRIED BY SAID BASE PLATE IN COVERING RELATION TO SAID APERTURE, SAID SEAL PLATE BEING PROVIDED WITH A CENTRAL APERTURE SLIDABLY RECEIVING SAID TUBE, SAID METERING STRUCTURE FURTHER INCLUDING A LOWER END PLATE DISPOSED BENEATH SAID PISTON BASE PLATE, MEANS INTERCONNECTING SAID FIRST MENTIONED SEAL PLATE AND SAID LOWER SEAL PLATE HOLDING SAID PLATES IN FIXED POSITION ONE WITH RESPECT TO THE OTHER SUCH THAT THE SEPARATION BETWEEN THE OPPOSED FACES THEREOF IS GREATER THAN THE THICKNESS OF SAID BASE PLATE, AND ABUTMENT MEANS CONNECTED TO THE LOWER PORTION OF SAID METERING STRUCTURE ADAPTED TO ENGAGE A PART FIXED IN RELATION TO THE BASE OF THE CYLINDER WHEN THE PISTON IS LOWERED THEREBY HOLDING THE LOWER SURFACE OF SAID FIRST MENTIONED SEAL PLATE ABOVE SAID BASE PLATE; AND A BUOYANT VALVE MEMBER HAVING A LONGITUDINAL BORE SLIDABLY RECEIVING SAID TUBE AND ADAPTED TO FLOAT IN THE LIQUID ABOVE SAID SEAL PLATE, SAID VALVE MEMBER HAVING A LOWER SURFACE PORTION ADAPTED TO ENGAGE THE TOP SURFACE OF SAID SEAL PLATE IN SURROUNDING RELATION TO THE APERTURE THEREIN WHEN THE LIQUID IN SAID PISTON FALLS TO A LOW LEVEL, AND MEANS PREVENTING THE PASSAGE OF LIQUID THROUGH THE BORE IN SAID VALVE MEMBER WHEN SAID VALVE MEMBER ENGAGES SAID SEAL PLATE. 